PROJECT SUMMARY Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN), are severe, life-threatening immunologically mediated adverse drug reactions representing the same disease across a spectrum of severity.1 There is currently no evidence-based standard of care treatment for SJS/TEN. Preventive efforts have been fueled by strong associations between the HLA Class I allele HLA-B*15:02 which has led to implementation of cost-effective pre-treatment genetic screening programs in many Southeast Asian countries.2,3 However, the lower prevalence (<1%) and negative predictive value of this HLA allele in European American, Hispanic American, and African American populations, and the lack of currently defined HLA associations with drugs commonly used and associated with SJS/TEN in the United States has left many evidence gaps and implementation hurdles.4 The scientific premise of this study is that the most efficacious treatment will impact cellular immune responses mediating, related biomarkers and clinical outcomes of SJS/TEN. We have assembled the North American Therapeutics in Epidermal Necrolysis Syndrome (NATIENS) study, a group of 22 sites across the United States to conduct the first multicenter double-blind double dummy randomized controlled assessment of cyclosporine or etanercept or supportive care. The controlled design will afford the opportunity to collect and assay multiple samples in each treatment arm, in both the acute and convalescent phase, with the aim to discover new strategies for prevention, early diagnosis and targeted treatment. We will use integrated multi-omic, single-cell and high-throughput in-vitro screening approaches to determine the genetic basis, immunopathology and antigen specificity of drug-induced SJS/TEN. In Specific Aim 1 we will establish the most clinically effective therapy for SJS/TEN through the NATIENS multi-centered, double-blind double-dummy randomized controlled trial with a planned accrual of 267 patients over 5 enrollment years to determine whether etanercept and/or cyclosporine have benefit over supportive care for the measured primary outcome of complete re-epithelialization. In Specific Aim 2 we will use genome-wide sequencing, high-resolution HLA sequencing, transcriptomic, and cytokine profiling to identify genetic and biological markers that predict risk and outcome for SJS/TEN. In Specific Aim 3 We will study the immune phenotype of cells in the skin, blister fluid and peripheral blood in acute SJS/TEN based on single-cell RNA and protein expression. Using the dominantly represented T-cell receptor (TCR) in the blister fluid we will use a high throughput in-vitro screening approach to identify specific epitopes recognized by CD8+ T cells at the site of SJS/TEN tissue damage.5 Our study will be the first to examine in a double-blind randomized controlled design both management and mechanisms of SJS/TEN. This will lead to new ways to prevent, diagnosis and treat SJS/TEN, and will create a roadmap and evidence-base for studies of serious immunologically-mediated adverse drug reactions and other immunologically-mediated diseases.